Certain beverage preparation machines use capsules containing ingredients to be extracted or to be dissolved; for other machines, the ingredients are stored and dosed automatically in the machine or else are added at the time of preparation of the drink.
Various beverage machines, such as coffee machines, are arranged to circulate liquid, usually water, from a water source that is cold or heated by heating means, to a mixing or infusion chamber where the beverage is actually prepared by exposing the circulating liquid to a bulk or pre-packaged ingredient, for instance within a capsule. From this chamber, the prepared beverage is usually guided to a beverage dispensing area, for instance to a beverage outlet located above a cup or mug support area comprised or associated with the beverage machine. During or after the preparation process, used ingredients and/or their packaging is evacuated to a collection receptacle.
Most coffee machines possess filling means that include a pump for liquid, usually water, which pumps the liquid from a source of water that is cold or indeed heated through heating means, such as a heating resistor, a thermoblock or the like. For instance, U.S. Pat. No. 5,943,472 discloses a water circulation system for such a machine between a water reservoir and a hot water or vapour distribution chamber, for an espresso machine. The circulation system includes valves, a metallic heating tube and a pump that are interconnected with each other and with the reservoir via a plurality of silicone hoses that are joined together by clamping collars.
To control the characteristics of the liquid circulated to the mixing or infusion chamber, e.g. quantity and/or speed, such machines typically include a flowmeter. The flowmeters used in such beverage machines are made of food safe materials at least where exposed to the circulating fluid and have to be economically affordable to be used in such machines.
For instance, EP 0 841 547 discloses a flowmeter commercialised by DIGMESA which is suitable for beverage preparation machines. This flowmeter has a two-part housing with a bayonet connection, the housing containing an inner measuring chamber with a central fixed shaft extending therethrough for mounting an inner rotatable measuring body with fins that are located in the flow path and that are driven thereby. The flow of liquid passing through the measuring chamber is derived from a measure of the speed of rotation of the rotatable measuring body using a Hall sensor. A drawback of this device lies in the large friction surface between the fixed shaft and the rotating measuring body which changes depending on the orientation of the flowmeter and which also affects the accuracy of the measure of the flow through the chamber.
U.S. Pat. No. 4,666,061 discloses a similar flowmeter for beverage dispenser lines for wine, mineral water or beer that can be easily disassembled and reassembled for cleaning. The flowmeter has a two-part housing assembled by a bayonet connector and enclosing a measuring chamber. The chamber contains a centred rotatable measuring body having a rotatable shaft held in pace by a pair of facing diamond point bearings mounted into the housing and extending into the chamber. A drawback of this device lies in the price of the diamond point bearings and the required assembly steps for mounting such point bearings into the housing of the flowmeter.
Hence, there is still a need to provide an accurate inexpensive flowmeter, in particular for use in a beverage preparation machine.